Communications method and apparatus

ABSTRACT

This application discloses a communications method and apparatus. The method includes: receiving, by a radio access network (RAN) node, a first message from an access and mobility management function (AMF) node, where the first message includes specified area related information of a terminal device, and the specified area related information is used to indicate a specified area of the terminal device; and when the RAN node determines, based on the specified area related information and first location information of the terminal device, that the terminal device moves out of the specified area, sending, by the RAN node, the first location information or first indication information to the AMF node or an SMF node, where the first indication information is used to indicate that the terminal device already moves out of the specified area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN 2018/080969, filed on Mar. 28, 2018, which claims priority toChinese Patent Application No. 201710698733.0, filed on Aug. 15, 2017.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of wireless communicationstechnologies, and in particular, to a communications method andapparatus.

BACKGROUND

A concept of a local area data network (LADN) is introduced in a 5Gsystem. A terminal device can access an LADN only when the terminaldevice is within an LADN service area (LADN SA); otherwise, the terminaldevice cannot access the LADN.

When a data network (DN) node has downlink data, for example, downlinkLADN data, to be sent to the terminal device, the DN node sends theto-be-sent downlink data to a radio access network (RAN) node by using auser plane function (UPF) node, and then the RAN node sends the data tothe terminal device.

However, the LADN SA may be different from a service scope of the RANnode. As shown in FIG. 1, when the terminal device is at a location 1,it indicates that the terminal device is within both the LADN SA and theservice scope of the RAN node. In this case, when receiving the downlinkLADN data specific to the terminal device, the RAN node may send thedownlink LADN data to the terminal device. However, when the terminaldevice moves from the location 1 to a location 2, it may be learnedthat, the terminal device already moves out of the LADN SA, but is stillwithin the service scope of the RAN. In this case, if the RAN nodereceives the downlink LADN data specific to the terminal device, the RANnode still sends the downlink LADN data to the terminal device.Consequently, the terminal device can still receive the downlink LADNdata after moving out of the LADN SA.

SUMMARY

Embodiments of this application provide a communications method, toresolve a problem that a terminal device can still receive downlink LADNdata when moving out of an LADN SA.

To achieve the foregoing objectives, the following technical solutionsare used in the embodiments of this application:

According to a first aspect, an embodiment of this application providesa communications method. The method includes: receiving, by a radioaccess network RAN node, a first message from an access and mobilitymanagement function AMF node, where the first message includes specifiedarea related information of a terminal device, and the specified arearelated information is used to indicate a specified area of the terminaldevice; and when the RAN node determines, based on the specified arearelated information and first location information of the terminaldevice, that the terminal device moves out of the specified area,sending, by the RAN node, the first location information or firstindication information to the AMF node or a session management functionSMF node, where the first indication information is used to indicatethat the terminal device already moves out of the specified area.

According to the method, the AMF node may send the specified arearelated information of the terminal device to the RAN node, and further,when determining that the terminal device moves out of the specifiedarea, the RAN node may send the first location information or the firstindication information to the AMF node or the SMF node, so that the AMFnode or the SMF node can learn that the terminal device already movesout of the specified area, thereby ensuring that a specified service canbe implemented only within the specified area. For example, if thespecified area is an LADN SA, when determining that the terminal devicemoves out of the LADN SA, the RAN node notifies the AMF node or the SMFnode that the terminal device already moves out of the LADN SA, and theSMF node can trigger a process of releasing a PDU session resource,thereby ensuring that the terminal device does not receive or send LADNdata after moving out of the LADN SA.

In a possible design, the specified area is a local area data networkservice area LADN SA, a location reporting area, or an area of interestof the SMF node.

In a possible design, before the determining, by the RAN node based onthe specified area related information and first location information ofthe terminal device, that the terminal device moves out of the specifiedarea, the method further includes: when the RAN node determines toswitch the terminal device from a Radio Resource Control RRC connectedstate to a Radio Resource Control inactive RRC inactive state,determining, by the RAN node, a radio access network notification areaRNA of the terminal device based on second location information of theterminal device and the specified area related information; and sending,by the RAN node, a second message to the terminal device, where thesecond message is used to release an RRC connection between the terminaldevice and the RAN node, and the second message carries the RNA.

According to the communications method, the RAN node determines the RNAwith reference to the specified area related information, so that thedetermined RNA is included in the specified area. Therefore, a case inwhich the terminal device moves out of the specified area but is stillwithin the RNA is avoided, and when the specified area is the LADN SA, aproblem that the terminal device in the RRC inactive state can stillreceive LADN data after moving out of the LADN SA is avoided.

In a possible design, the specified area related information includes alocation area identifier list corresponding to the specified area; and aspecific implementation method of determining, by the RAN node, an RNAof the terminal device based on second location information of theterminal device and the specified area related information is:

when a location indicated by the second location information is withinan area indicated by the location area identifier list corresponding tothe specified area, determining, by the RAN node, the RNA based on firstreference information, where the RNA is included in the specified area,and the first reference information includes at least registration areainformation of the terminal device. It may be learned that, because theRNA is included in the specified area, the case in which the terminaldevice moves out of the specified area but is still within the RNA isavoided, and the problem that the terminal device can still receive LADNdata within the RNA after moving out of the LADN SA can be avoided.

In a possible design, the specified area related information includesLADN SA related information, and the LADN SA related informationincludes a data network name DNN corresponding to the LADN SA; and

a specific implementation method of determining, by the RAN node, an RNAof the terminal device based on second location information of theterminal device and the specified area related information is:

determining, by the RAN node based on the DNN and a mapping relationshipbetween the DNN and a location area identifier list corresponding to theLADN SA, the location area identifier list corresponding to the LADN SA;and when a location indicated by the second location information iswithin an area indicated by the location area identifier listcorresponding to the LADN SA, determining, by the RAN node, the RNAbased on second reference information, where the second referenceinformation includes at least registration area information of theterminal device, and the RNA is included in the LADN SA.

In a possible design, before the determining, by the RAN node based onthe specified area related information and first location information ofthe terminal device, that the terminal device moves out of the specifiedarea, the RAN node may receive a third message from the terminal device,where the third message is used to request, when the terminal devicemoves out of the RNA, to restore the RRC connection between the terminaldevice and the RAN node; and then the RAN node updates locationinformation of the terminal device to the first location information.

In a possible design, the determining, by the RAN node based on thespecified area related information and first location information of theterminal device, that the terminal device moves out of the specifiedarea includes:

when a location indicated by the first location information is withinnone of areas indicated by location area identifiers in the locationarea identifier list corresponding to the specified area, determining,by the RAN node, that the terminal device moves out of the specifiedarea.

According to a second aspect, an embodiment of this application providesa communications method, including: receiving, by a radio access networkRAN node, a first message from an access and mobility managementfunction AMF node, where the first message is used to instruct, when theRAN node determines to switch a terminal device from a Radio ResourceControl RRC connected state to a Radio Resource Control inactive RRCinactive state, to send, to the AMF node, a notification message used tonotify a state of the terminal device; and when the RAN node determinesto switch the terminal device from the RRC connected state to the RRCinactive state, sending, by the RAN node, the notification message tothe AMF node based on the first message.

According to the communications method, the AMF node may notify the RANnode in advance; when it is determined that the terminal device is to beswitched from the RRC connected state to the RRC inactive state, thenotification message used to notify the state of the terminal deviceneeds to be sent to the AMF node; then the AMF node sends, to an SMFnode, the notification message used to notify the state of the terminaldevice; and when receiving the notification message, the SMF node candetermine that the terminal device is already in the RRC inactive state,and does not send LADN data to the terminal device, thereby avoiding aproblem that the terminal device in the RRC inactive state can stillreceive LADN data after moving out of an LADN SA.

In a possible design, the first message carries first indicationinformation, and the first indication information is used to instruct,when the RAN node determines to switch the terminal device from the RRCconnected state to the RRC inactive state, the RAN node to send thenotification message to the AMF node.

In a possible design, the first indication information includesspecified area related information, and the specified area relatedinformation is used to indicate a specified area of the terminal device.

In a possible design, the specified area is a local area data networkservice area LADN SA, a location reporting area, or an area of interestof a session management function SMF node.

In a possible design, the specified area related information includes alocation area identifier list corresponding to the specified area; or

the specified area related information includes LADN SA relatedinformation, and the LADN SA related information includes a locationarea identifier list corresponding to the LADN SA; or

the specified area related information includes LADN SA relatedinformation, and the LADN SA related information includes a data networkname DNN corresponding to the LADN SA.

In a possible design, after the RAN node receives the first message fromthe AMF node, when the RAN node determines to switch the terminal devicefrom the RRC connected state to the RRC inactive state, the RAN nodedetermines a radio access network notification area RNA of the terminaldevice based on location information of the terminal device; and thenthe RAN node sends a second message to the terminal device, where thesecond message is used to instruct the terminal device to release an RRCconnection to the RAN node, and the second message carries the RNA.

In a possible design, after the RAN node sends the notification messageto the AMF node based on the first message, the RAN node may receive athird message from the AMF node, where the third message carries apacket data unit PDU session identifier, and the third message is usedto instruct the RAN node to release a PDU session resource correspondingto the PDU session identifier; and then the RAN node releases the PDUsession resource based on the third message.

According to the method, when determining that the state of the terminaldevice is the RRC inactive state, the SMF node may instruct a UPF nodeto release the PDU session resource, and further instruct, by exchangingsignaling, the RAN node to release the PDU session resource. In thisway, when the terminal device moves out of the specified area, there isno PDU session resource used for sending related service data. Forexample, the problem that the terminal device can still receive LADNdata when moving out of the LADN SA is avoided.

In a possible design, the first message carries the specified arearelated information, and the specified area related information is usedto indicate the specified area of the terminal device; and the methodfurther includes: receiving, by the RAN node, a fourth message from theAMF node, where the fourth message is used to request to establish theRRC connection between the terminal device and the RAN node; theninstructing, by the RAN node, the terminal device to establish the RRCconnection between the terminal device and the RAN node; and further,when the RAN node determines, based on the specified area relatedinformation and the location information of the terminal device, thatthe terminal device moves out of the specified area, sending, by the RANnode, the location information of the terminal device or the firstindication information to the AMF node or the SMF node, where the firstindication information is used to indicate that the terminal devicealready moves out of the specified area.

According to the communications method, when obtaining downlink data ofthe terminal device, the UPF node notifies the RAN node by using the SMFnode and the AMF node, so that the RAN node instructs the terminaldevice to establish the RRC connection between the terminal device andthe RAN node, and further, the RAN node may determine the locationinformation of the terminal device, and if the RAN node determines,based on the location information of the terminal device, that theterminal device already moves out of the specified area, the RAN nodereports related information or a related message to the AMF node or theSMF node, so that the SMF node instructs the UPF node to releasedownlink LADN data or prolong buffering of downlink LADN data, therebyensuring that the terminal device does not receive the downlink LADNdata when moving out of the specified area.

According to a third aspect, an embodiment of this application providesa communications method, including: determining, by a radio accessnetwork RAN node, that a terminal device switches from a Radio ResourceControl RRC connected state to a Radio Resource Control inactive RRCinactive state; and then sending, by the RAN node to an access andmobility management function AMF node, a notification message used tonotify a state of the terminal device.

According to the method, when determining that the terminal deviceswitches from the RRC connected state to the RRC inactive state, the RANnode sends, to the AMF node, the notification message used to notify thestate of the terminal device; and when receiving the notificationmessage, the AMF node can determine that the terminal device is alreadyin the RRC inactive state, and does not send LADN data to the terminaldevice, thereby avoiding a problem that the terminal device in the RRCinactive state can still receive LADN data after moving out of an LADNSA.

In a possible design, before the RAN node determines that the terminaldevice switches from the RRC connected state to the RRC inactive state,the RAN node may determine a radio access network notification area RNAof the terminal device based on location information of the terminaldevice; and then the RAN node sends a first message to the terminaldevice, where the first message is used to instruct the terminal deviceto release an RRC connection to the RAN node, and the first messagecarries the RNA.

According to a fourth aspect, an embodiment of this application providesa communications method, including: sending, by an access and mobilitymanagement function AMF node, a first message to a radio access networkRAN node, where the first message is used to instruct, when the RAN nodedetermines to switch a terminal device from a Radio Resource Control RRCconnected state to a Radio Resource Control inactive RRC inactive state,the RAN node to send, to the AMF node, a first notification message usedto notify a state of the terminal device; receiving, by the AMF node,the first notification message from the RAN node; and then sending, bythe AMF node, a second notification message to a session managementfunction SMF node based on the first notification message, where thesecond notification message is used to notify the SMF node of the stateof the terminal device.

In a possible design, after the AMF node sends the second notificationmessage to the SMF node, the AMF node may receive a second message fromthe SMF node, where the second message carries a packet data unit PDUsession identifier, and the second message is used to instruct the AMFnode to instruct the RAN node to release a PDU session resourcecorresponding to the PDU session identifier; and then the AMF node sendsa third message to the RAN node, where the third message carries the PDUsession identifier, and the third message is used to instruct the RANnode to release the PDU session resource corresponding to the PDUsession identifier.

In a possible design, the AMF node may send a fourth message to the RANnode, where the fourth message is used to request to establish an RRCconnection between the terminal device and the RAN node.

In a possible design, after the AMF node sends the fourth message to theRAN node, the AMF node may receive location information of the terminaldevice from the RAN node, and when determining, based on specified arearelated information and the location information of the terminal device,that the terminal device moves out of the specified area, the AMF nodesends first indication information to the SMF node, where the firstindication information is used to indicate that the terminal devicealready moves out of the specified area, and the specified area relatedinformation is used to indicate the specified area of the terminaldevice; or

the AMF node receives first indication information from the RAN node,and sends the first indication information to the SMF node, where thefirst indication information is used to indicate that the terminaldevice already moves out of a specified area of the terminal device; or

the AMF node receives a response message of the fourth message from theRAN node, where the response message of the fourth message is used bythe RAN node to reject establishment of the RRC connection between theterminal device and the RAN node.

According to a fifth aspect, an embodiment of this application providesa communications method, including: receiving, by a session managementfunction SMF node, a notification message that is from an access andmobility management function AMF node and that is used to notify a stateof the terminal device; when the notification message is used to notifythat the state of the terminal device is a Radio Resource Controlinactive RRC inactive state, sending, by the SMF node, a first messageto a user plane function UPF node, where the first message is used torequest the UPF node to release a packet data unit PDU session resourceof the terminal device; receiving, by the SMF node, a second messagefrom the UPF node, where the second message is used to notify the SMFnode that the UPF node already releases the PDU session resource of theterminal device, and the second message carries a PDU session identifierof a PDU session of the terminal device; and sending, by the SMF node, athird message to the AMF node, where the third message carries the PDUsession identifier, and the third message is used to trigger the AMFnode to instruct the RAN node to release a PDU session resourcecorresponding to the PDU session identifier.

According to a sixth aspect, an embodiment of this application providesa communications apparatus. The apparatus can implement a functionperformed by the RAN node according to the first aspect, and thefunction may be implemented by hardware or may be implemented byexecuting corresponding software by hardware. The hardware or thesoftware includes one or more modules corresponding to the foregoingfunction.

In a possible design, a structure of the apparatus includes a processorand a communications interface. The processor is configured to supportthe apparatus to perform a corresponding function in the foregoingmethod. The communications interface is configured to supportcommunication between the apparatus and another network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and stores a program instruction and data thatare required by the apparatus.

According to a seventh aspect, an embodiment of this applicationprovides a communications apparatus. The apparatus can implement afunction performed by the RAN node according to the second aspect, andthe function may be implemented by hardware or may be implemented byexecuting corresponding software by hardware. The hardware or thesoftware includes one or more modules corresponding to the foregoingfunction.

In a possible design, a structure of the apparatus includes a processorand a communications interface. The processor is configured to supportthe apparatus to perform a corresponding function in the foregoingmethod. The communications interface is configured to supportcommunication between the apparatus and another network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and stores a program instruction and data thatare required by the apparatus.

According to an eighth aspect, an embodiment of this applicationprovides a communications apparatus. The apparatus can implement afunction performed by the RAN node according to the third aspect, andthe function may be implemented by hardware or may be implemented byexecuting corresponding software by hardware. The hardware or thesoftware includes one or more modules corresponding to the foregoingfunction.

In a possible design, a structure of the apparatus includes a processorand a communications interface. The processor is configured to supportthe apparatus to perform a corresponding function in the foregoingmethod. The communications interface is configured to supportcommunication between the apparatus and another network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and stores a program instruction and data thatare required by the apparatus.

According to a ninth aspect, an embodiment of this application providesa communications apparatus. The apparatus can implement a functionperformed by the AMF node according to the fourth aspect, and thefunction may be implemented by hardware or may be implemented byexecuting corresponding software by hardware. The hardware or thesoftware includes one or more modules corresponding to the foregoingfunction.

In a possible design, a structure of the apparatus includes a processorand a communications interface. The processor is configured to supportthe apparatus to perform a corresponding function in the foregoingmethod. The communications interface is configured to supportcommunication between the apparatus and another network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and stores a program instruction and data thatare required by the apparatus.

According to a tenth aspect, an embodiment of this application providesa communications apparatus. The apparatus can implement a functionperformed by the SMF node according to the fifth aspect, and thefunction may be implemented by hardware or may be implemented byexecuting corresponding software by hardware. The hardware or thesoftware includes one or more modules corresponding to the foregoingfunction.

In a possible design, a structure of the apparatus includes a processorand a communications interface. The processor is configured to supportthe apparatus to perform a corresponding function in the foregoingmethod. The communications interface is configured to supportcommunication between the apparatus and another network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and stores a program instruction and data thatare required by the apparatus.

According to an eleventh aspect, an embodiment of this applicationprovides a communications system. The system includes the terminaldevice, the RAN node, the AMF node, the SMF node, and the UPF nodeaccording to the first aspect to the fifth aspect.

According to a twelfth aspect, a program is provided. When beingexecuted by a processor, the program is configured to perform any methodaccording to the first aspect.

According to a thirteenth aspect, a program is provided. When beingexecuted by a processor, the program is configured to perform any methodaccording to the second aspect.

According to a fourteenth aspect, a program is provided. When beingexecuted by a processor, the program is configured to perform any methodaccording to the third aspect.

According to a fifteenth aspect, a program is provided. When beingexecuted by a processor, the program is configured to perform any methodaccording to the fourth aspect.

According to a sixteenth aspect, a program is provided. When beingexecuted by a processor, the program is configured to perform any methodaccording to the fifth aspect.

According to a seventeenth aspect, a computer readable storage medium isprovided, including the program according to the twelfth aspect.

According to an eighteenth aspect, a computer readable storage medium isprovided, including the program according to the thirteenth aspect.

According to a nineteenth aspect, a computer readable storage medium isprovided, including the program according to the fourteenth aspect.

According to a twentieth aspect, a computer readable storage medium isprovided, including the program according to the fifteenth aspect.

According to a twenty-first aspect, a computer readable storage mediumis provided, including the program according to the sixteenth aspect.

According to a twenty-second aspect, a RAN node is provided, includingat least one processing element or chip configured to perform any methodaccording to the first aspect.

According to a twenty-third aspect, a RAN node is provided, including atleast one processing element or chip configured to perform any methodaccording to the second aspect.

According to a twenty-fourth aspect, a RAN node is provided, includingat least one processing element or chip configured to perform any methodaccording to the third aspect.

According to a twenty-fifth aspect, an AMF node is provided, includingat least one processing element or chip configured to perform any methodaccording to the fourth aspect.

According to a twenty-sixth aspect, a RAN node is provided, including atleast one processing element or chip configured to perform any methodaccording to the fifth aspect.

Compared with the prior art, the AMF node may send the specified arearelated information of the terminal device to the RAN node, and further,when determining that the terminal device moves out of the specifiedarea, the RAN node may send the first location information or the firstindication information to the AMF node or the SMF node, so that the AMFnode or the SMF node can learn that the terminal device already movesout of the specified area, thereby ensuring that the specified servicecan be implemented only within the specified area. For example, if thespecified area is the LADN SA, when determining that the terminal devicemoves out of the LADN SA, the RAN node notifies the AMF node or the SMFnode that the terminal device already moves out of the LADN SA, and theSMF node can trigger the process of releasing the PDU session resource,thereby ensuring that the terminal device does not receive or send theLADN data after moving out of the LADN SA.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example of a location of a terminaldevice provided in the Background;

FIG. 2 is a schematic diagram of a network architecture according to anembodiment of this application;

FIG. 3 is a schematic structural diagram of a communications systemaccording to an embodiment of this application;

FIG. 4 is a schematic structural diagram of another communicationssystem according to an embodiment of this application;

FIG. 5 is a schematic diagram of an example of a movement process of aterminal device according to an embodiment of this application;

FIG. 6 is a flowchart of a communications method according to anembodiment of this application;

FIG. 7 is a flowchart of another communications method according to anembodiment of this application;

FIG. 8 is a schematic diagram of an example of an RNA according to anembodiment of this application;

FIG. 9 is a flowchart of another communications method according to anembodiment of this application;

FIG. 10 is a flowchart of another communications method according to anembodiment of this application;

FIG. 11 is a flowchart of another communications method according to anembodiment of this application;

FIG. 12 is a flowchart of another communications method according to anembodiment of this application;

FIG. 13 is a flowchart of another communications method according to anembodiment of this application;

FIG. 14 is a flowchart of another communications method according to anembodiment of this application;

FIG. 15 is a schematic structural diagram of a RAN node according to anembodiment of this application;

FIG. 16 is a schematic structural diagram of another RAN node accordingto an embodiment of this application;

FIG. 17 is a schematic structural diagram of another RAN node accordingto an embodiment of this application;

FIG. 18 is a schematic structural diagram of an AMF node according to anembodiment of this application;

FIG. 19 is a schematic structural diagram of an SMF node according to anembodiment of this application;

FIG. 20 is a schematic structural diagram of a RAN node according to anembodiment of this application;

FIG. 21 is a schematic structural diagram of an AMF node according to anembodiment of this application; and

FIG. 22 is a schematic structural diagram of an SMF node according to anembodiment of this application.

DESCRIPTION OF EMBODIMENTS

Network architectures and service scenarios described in thisapplication more clearly describe the technical solutions in thisapplication, but are not intended to limit the technical solutionsprovided in this application. A person of ordinary skill in the art mayknow that as the network architectures evolve and a new businessscenario emerges, the technical solutions provided in this applicationfurther apply to a similar technical problem.

It should be noted that the term “exemplary” or “for example” in thisapplication means “used as an example, an illustration, or adescription. Any embodiment or design scheme described as “exemplary” or“for example” in this application should not be explained as being morepreferred or having more advantages than another embodiment or designscheme. Exactly, use of the term “example” is intended to present aconcept in a specific manner.

In this application, “of”, “relevant” and “corresponding” may be mixedduring use. It should be noted that, when there is no need to emphasizea difference thereof, meanings expressed by them are the same.

As shown in FIG. 2, FIG. 2 shows a network structure. The networkstructure is applicable to a next generation communications system.Various components in the network structure are briefly described below:

A terminal device may include various handheld devices, in-vehicledevices, wearable devices, or computing devices that have a wirelesscommunication function, or another processing device connected to awireless modem, and various forms of terminals, mobile stations (MS),user equipment (UE), software clients, and the like, for example, awater meter, an electricity meter, or a sensor.

A RAN node is similar to a base station in a conventional network,provides a network access function to an authorized user within aspecified area, and can use transmission tunnels of different qualitybased on user levels, service requirements, and the like. The RAN canmanage a radio resource and provide an access service to a terminaldevice, to complete forwarding of a control signal and user data betweenthe terminal device and a core network.

An access and mobility management function (AMF) node is responsible formobility management, access management, and the like, and may beconfigured to implement a function in a mobility management entity (MME)function other than a session management function, for example, a lawfulinterception function and an access authorization function.

A session management function (SMF) node is configured to establish asession for the terminal device, allocate a session identifier (ID),manage and allocate an Internet Protocol (IP) address of a terminaldevice, and manage or terminate a session.

A data network (DN) is a network configured to provide external data,for example, the Internet.

A control plane function (CPF) node is mainly configured to performaccess control and mobility management functions (for example, functionsof an AMF) such as authentication, encryption, and location registrationon a terminal device, and perform session management functions (forexample, functions of an SMF) such as establishment, release, and changeof a user plane transmission path. For ease of understanding, the CPFnode may be considered as a set including network elements such as theAMF node and the SMF node.

An N2 interface is a reference point between the (R)AN node and the AMFnode and is configured to send a non-access stratum (NAS) message or thelike.

An N3 interface is a reference point between the (R)AN node and the UPFnode and is configured to transmit user plane data or the like.

An N4 interface is a reference point between the SMF node and the UPFnode and is configured to transmit information such as tunnel identifierinformation of an N3 connection, data buffering indication information,and a downlink data notification message.

An N6 interface is a reference point between the UPF node and a DN nodeand is configured to transmit user plane data or the like.

For ease of understanding, related technologies in this application aredescribed as follows:

A connected state of a terminal device is a connectionmanagement-connected (CM-CONNECTED) state. The CM-connected stateincludes a Radio Resource Control connected (RRC Connected) state and aRadio Resource Control inactive (RRC inactive) state.

As shown in FIG. 3, FIG. 3 is a simplified architectural diagram of acommunications system. When a terminal device needs to exchange datawith a core network, the terminal device is in an RRC connected state, aRAN node is connected to a CPF node by using an N2 interface, and theRAN node is connected to a UPF by using an N3 interface. When theterminal device is in the RRC connected state, the RAN node may sense acell that the terminal device camps on and location information of theterminal device, and a network element (for example, an AMF node) in theCPF node may sense the RAN node connected to the terminal device. InFIG. 3, when downlink data in a DN is transmitted to the UPF node, theUPF node may send the downlink data to the RAN node connected to theterminal device, and then the RAN node sends the downlink data to theterminal device.

When the terminal device in the RRC connected state performs no datatransmission within a preset time period, the RAN node determines,according to a preset policy, whether the terminal device should beswitched from the RRC connected state to an RRC inactive state. When theterminal device is in the RRC inactive state, as shown in FIG. 4, an RRCconnection between the terminal device and the RAN node is released, andan N2 connection between the RAN node and the CPF node and an N3connection between the RAN node and the UPF are kept. When the RAN nodedetermines to switch the terminal device from the RRC connected state tothe RRC inactive state, the RAN node sets a radio access networknotification area (RAN Notification Area, RNA) for the terminal devicebased on the location information of the terminal device, and then sendsan RRC connection release message to the terminal device. The RRCconnection release message carries the RNA. After receiving the RRCconnection release message, the terminal device releases the RRCconnection to the RAN node, and stores the RNA. In the RRC inactivestate, no signaling is exchanged between the RAN node and the terminaldevice, so that the RAN node cannot sense the location information ofthe terminal device. During movement of the terminal device, theterminal device senses cell information broadcast by a base station, anddetermines the location information of the terminal device. Whendetermining that the terminal device moves out of the RNA, the terminaldevice sends an RRC connection restoration request to the RAN node, tore-establish the RRC connection to the RAN node. If the RAN determinesthat the terminal device still needs to be switched to the RRC inactivestate, the RAN re-determines an RNA of the terminal device based onnewest location information of the terminal device.

It should be noted that, the RNA that is set by the RAN node for theterminal device may be smaller than an actual service scope of the RANnode. In this way, when the terminal device moves out of the RNA that isset by the RAN node for the terminal device, the terminal device canstill access the same RAN node, and then the RAN node re-sets an RNA forthe terminal device. Alternatively, after moving out of the RNA that isset by the RAN node for the terminal device, the terminal device mayaccess another RAN, and the another RAN sets an RNA for the terminaldevice.

In addition, when the terminal device is in the RRC inactive state,because the N2 connection still exists between the CPF node and the RANnode, the CPF node still considers that the terminal device is in theconnected state; when receiving downlink data specific to the terminaldevice, the UPF node still sends the downlink data to the RAN node;after receiving the downlink data, the RAN node initiates paging to theterminal device within the RNA; and after receiving a paging messagefrom the RAN node, the terminal device is switched to the RRC connectedstate again, and then the RAN node sends the downlink data to theterminal device.

When the terminal device accesses an LADN, if the terminal device needsto send uplink LADN data, and the terminal device already establishes apacket data unit (Packet Data Unit, PDU) session transmission channel tothe LADN, the terminal device may send the uplink LADN data by using aPDU session resource. When sensing that the terminal device moves out ofan LADN SA, a network element in the CPF node releases the PDU sessionresource. However, when the terminal device needs to send uplink LADNdata, but no PDU session transmission channel exists between theterminal device and the LADN, if the terminal device determines that theterminal device is within the LADN SA, the terminal device sends, to theCPF node, a request for establishing a PDU session transmission channel.In addition, the RAN node reports, to the CPF node, information about acell to which the terminal device belongs; and then the CPF node maydetermine the location information of the terminal device, anddetermine, based on the location information of the terminal device,whether the terminal device is within the LADN SA. If the CPF nodedetermines that the terminal device is within the LADN SA, the CPF nodeallows establishment of the PDU session transmission channel, so thatthe terminal device sends the uplink LADN data by using a PDU sessionresource.

When the terminal device accesses the LADN, if the UPF node receivesdownlink LADN data specific to the terminal device, and the terminaldevice already establishes a PDU session transmission channel to theLADN (to be specific, a user plane resource for a PDU session in theLADN is established), the UPF node may send the downlink LADN data tothe RAN node, and then the RAN node sends the LADN data to the terminaldevice. However, if the UPF node receives downlink LADN data specific tothe terminal device, but no PDU session transmission channel existsbetween the terminal device and the LADN, the UPF node may send adownlink data notification (Downlink Data Notification, DDN) message toan SMF node. After receiving the DDN message, the SMF node obtains thelocation information of the terminal device by using the AMF node, ifthe SMF node determines, based on the location information of theterminal device, that the terminal device is within the LADN SA, the SMFnode triggers a process of establishing a PDU session transmissionchannel, so that after the PDU session channel is established, the UPFnode may send the downlink LADN data to the terminal device by using theRAN node.

With reference to the foregoing descriptions, when the RAN receives thedownlink data, if the RAN node determines that the terminal device is inthe RRC connected state or the RRC inactive state, and the terminaldevice is within the service scope of the RAN node, the RAN node maysend the downlink data to the terminal device. However, in the priorart, when sending the downlink data to the terminal device, the RAN nodedoes not consider whether the terminal device is within the LADN SA.Consequently, a problem that the downlink LADN data is still sent to theterminal device when the terminal device already moves out of the LADNSA occurs.

On one hand, when the terminal device is always in the RRC connectedstate, if the terminal device is within an area covered by both the LADNSA and the service scope of the RAN node, the RAN node may send thedownlink LADN data to the terminal device. If the terminal device in theRRC connected state moves out of the LADN SA but is still within theservice scope of the RAN node, if the RAN node receives the downlinkLADN data specific to the terminal device, because the RAN node does notknow the LADN SA, the RAN node cannot determine whether the terminaldevice is within the LADN SA at this time, and therefore, the RAN nodestill sends downlink LADN SA data to the terminal device. Consequently,a problem that the terminal device can still receive the downlink LADNdata after moving out of the LADN SA is caused.

On the other hand, as shown in FIG. 5, the terminal device is within anarea covered by both the LADN SA and the service scope of the RAN node.In this case, the terminal device is switched from the RRC connectedstate to the RRC inactive state. The RAN node sets the RNA for theterminal device, and then the terminal device moves out of the LADN SAbut is still within the RNA. Subsequently, the RAN node receives thedownlink LADN data specific to the terminal device, and pages theterminal device within the RNA. After receiving a paging message, theterminal device is switched from the RRC inactive state to the RRCconnected state, and then the RAN node sends the downlink LADN data tothe terminal device. It may be learned that, in this case, the terminaldevice is already not within the LADN SA, but still receives thedownlink LADN data.

To resolve the problem that the terminal device can still receive theLADN data after moving out of the LADN SA, a principle of thisapplication is as follows: In a process of establishing an N2 connectionto the RAN node, the AMF node sends LADN SA related information of theterminal device to the RAN, and then when determining, based on thelocation information of the terminal device and the LADN SA relatedinformation, that the terminal device moves out of the LADN SA, the RANnode may notify the AMF node or the SMF node that the terminal devicealready moves out of the LADN SA. In this way, the SMF node can releasethe PDU session resource of the terminal device or instruct the UPF nodeto prolong buffering of the downlink LADN SA data or discard thedownlink LADN SA data. In this way, the terminal device does not receivethe LADN data after moving out of the LADN SA.

As shown in FIG. 6, an embodiment of this application provides acommunications method. The method is applied to the communicationssystem shown in FIG. 2, and the method includes the following steps.

601: A RAN node receives a first message from an AMF node.

Correspondingly, the AMF node receives the first message.

The first message may be an N2 connection activation message sent by theAMF node in a process of activating an N2 connection between the RANnode and the AMF node. For example, the N2 connection activation messagemay be specifically a path switch response (Path Switch Response)message. Alternatively, the first message may be a dedicated messageused to carry specified area related information of the terminal device.Alternatively, the first message may be an N2 message sent by the AMFnode to the RAN node during establishment of a PDU session, or alocation reporting control message (Location Report Control message).

The first message includes the specified area related information of theterminal device, and the specified area related information is used toindicate a specified area of the terminal device. The specified area maybe specifically an LADN SA, or a location reporting area (LocationReporting area), or an area of interest (Area of interest). The area ofinterest may be an area that interests an SMF node.

Optionally, the specified area related information includes a locationarea identifier list corresponding to the specified area, for example, alocation area identifier list corresponding to the LADN SA, or alocation area identifier list corresponding to the location reportingarea.

The location area identifier list may be a cell identifier (Cell ID)list or may be a tracking area identity (TAI) list.

Optionally, the specified area related information includes LADN SArelated information, and the LADN SA related information may include alocation area identifier list corresponding to the LADN SA, or a datanetwork name (DNN) corresponding to the LADN SA.

The location area identifier list corresponding to the LADN SA may bespecifically a cell ID list or a tracking area list (TAL). The TAL mayinclude at least one TAI.

The LADN SA may be a range within which one or more LADNs provide aservice, and the DNN corresponding to the LADN SA may be names of theone or more LADNs.

For example, the specified area includes at least one location area, andthe location area may be one cell or one tracking area, so that thelocation area identifier list corresponding to the specified area may bespecifically a list including an identifier of the at least one locationarea included in the specified area. To be specific, the location areaidentifier list corresponding to the specified area is a list includinglocation area identifiers of location areas included in the specifiedarea. For example, it is assumed that the location area identifier listcorresponding to the specified area includes a cell identifier 1, a cellidentifier 2, and a cell identifier 3. It indicates that the specifiedarea is coverage of a cell indicated by the cell identifier 1, coverageof a cell indicated by the cell identifier 2, and coverage of a cellindicated by the cell identifier 3.

602: When the RAN node determines, based on specified area relatedinformation and first location information of a terminal device, thatthe terminal device moves out of a specified area, the RAN node sendsthe first location information or first indication information to theAMF node or an SMF node.

Correspondingly, the AMF node or the SMF node receives the firstlocation information or the first indication information.

The first indication information may be used to indicate that theterminal device already moves out of the specified area.

The first location information may be information about a cell that theterminal device camps on or information about a tracking area that theterminal device camps on when or after the terminal device is switchedfrom an RRC inactive state to an RRC connected state.

For example, when the terminal device is switched from the RRC inactivestate to the RRC connected state, the terminal device sends an RRCconnection restoration request to the RAN node. The RAN node can learn,by receiving the RRC connection restoration request, of informationabout a cell accessed by the terminal device, and then determine thefirst location information of the terminal device based on locationinformation of the cell. The first location information includes a cellidentifier of the cell accessed by the terminal device and a TAI.

A method for determining, by the RAN node based on the specified arearelated information and the first location information of the terminaldevice, that the terminal device moves out of the specified area in step602 may use the following two manners:

First manner: The specified area related information includes thelocation area identifier list corresponding to the specified area, andwhen a location indicated by the first location information is withinnone of areas indicated by location area identifiers in the locationarea identifier list corresponding to the specified area, the RAN nodedetermines that the terminal device moves out of the specified area.

On the contrary, when a location indicated by the first locationinformation is within an area indicated by any location area identifierin the location area identifier list corresponding to the specifiedarea, the RAN node may determine that the terminal device does not moveout of the specified area.

Second manner: The specified area related information includes the LADNSA related information, and the LADN SA related information includes adata network name DNN corresponding to the LADN SA. The RAN nodedetermines, based on the DNN, and a mapping relationship between a DNNand a location area identifier list corresponding to an LADN SA, thelocation area identifier list corresponding to the LADN SA. When alocation indicated by the first location information is within none ofareas indicated by location area identifiers in the location areaidentifier list corresponding to the LADN SA, the RAN node determinesthat the terminal device moves out of the specified area.

Specifically, the specified area is the LADN SA, and the LADN SA relatedinformation includes the DNN corresponding to the LADN SA. The RAN nodemay determine, based on the DNN included in the LADN SA relatedinformation, and the mapping relationship between a DNN and a locationarea identifier list corresponding to an LADN SA, the location areaidentifier list corresponding to the LADN SA.

For example, the mapping relationship between a DNN and a location areaidentifier list corresponding to an LADN SA is shown in Table 1.

TABLE 1 Location area identifier list 1 DNN 1 Location area identifierlist 2 DNN 2 Location area identifier list 3 DNN 3

If the LADN SA related information in the first message received by theRAN is the DNN 1, the RAN may find, based on Table 1, the location areaidentifier list 1 corresponding to the DNN 1, and may further determinethat a total area including areas indicated by location area identifiersin the location area identifier list 1 is the LADN SA.

It should be noted that, that the RAN node sends the first locationinformation or the first indication information to the AMF node or theSMF node may specifically include the following four cases:

First case: The RAN node sends the first location information to the AMFnode.

Correspondingly, the method may further include: after receiving thefirst location information, determining, by the AMF node, whether thelocation indicated by the first location information is within thespecified area, and if the AMF node determines that the locationindicated by the first location information is not within the specifiedarea, notifying, by the AMF node, the SMF node that the terminal devicealready moves out of the specified area.

Second case: The RAN node sends the first indication information to theAMF node.

Correspondingly, after the AMF node receives the first indicationinformation, the AMF node sends the first indication information to theSMF node.

Third case: The RAN node sends the first location information to the SMFnode.

Correspondingly, after receiving the first location information, the SMFnode determines whether the location indicated by the first locationinformation is within the specified area, and if the SMF node determinesthat the location indicated by the first location information is notwithin the specified area, the SMF node triggers a process of releasinga PDU session resource of the terminal device.

Fourth case: The RAN node sends the first indication information to theSMF node.

Correspondingly, the SMF node receives the first indication information,and when the first indication information indicates that the terminaldevice already moves out of the specified area, triggers a process ofreleasing a PDU session resource of the terminal device.

It should be noted that, the process of releasing the PDU sessionresource that is mentioned in the third case and the fourth case may bea process of releasing a PDU session or a process of deactivating a PDUsession.

According to the method provided in the foregoing embodiment, the AMFnode may send the specified area related information of the terminaldevice to the RAN node, and further, when determining that the terminaldevice moves out of the specified area, the RAN node may send the firstlocation information or the first indication information to the AMF nodeor the SMF node, so that the AMF node or the SMF node can learn that theterminal device already moves out of the specified area, therebyensuring that a specified service can be implemented only within thespecified area. For example, if the specified area is the LADN SA, whendetermining that the terminal device moves out of the LADN SA, the RANnode notifies the AMF node or the SMF node that the terminal devicealready moves out of the LADN SA, and the SMF node can trigger theprocess of releasing the PDU session resource, thereby ensuring that theterminal device does not receive or send LADN data after moving out ofthe LADN SA.

Optionally, in a first implementation scenario of the foregoingembodiment, as shown in FIG. 7, before step 602, the method furtherincludes step 701 to step 703.

701: When the RAN node determines to switch a terminal device from anRRC connected state to an RRC inactive state, the RAN node determines anRNA of the terminal device based on second location information andspecified area related information of the terminal device.

For example, the RAN node may determine, based on whether data istransmitted between the terminal device and the RAN node within aspecified time period, whether to switch the terminal device from theRRC connected state to the RRC inactive state. If no data is transmittedbetween the terminal device and the RAN node within the specified timeperiod, it is determined that the terminal device is to be switched fromthe RRC connected state to the RRC inactive state.

Further, the RAN node may determine, with reference to relatedparameters of the terminal device that are provided by the AMF node andwhether data is transmitted between the terminal device and the RAN nodewithin the specified time period, whether to switch the terminal devicefrom the RRC connected state to the RRC inactive state. The relatedparameters of the terminal device that are provided by the AMF node maybe parameters such as a registration area of the terminal device,discontinuous reception (DRX) information of the terminal device, andwhether the terminal device is in mobile initiated connection only(MICO) mode.

For example, when the terminal device is not in MICO mode, and no datais transmitted between the terminal device and the RAN node within thespecified time period, the RAN node determines to switch the terminaldevice from the RRC connected state to the RRC inactive state. If theterminal device is in MICO mode, the terminal device does not listen toa paging message, and the RAN node does not page the terminal device, sothat the terminal device is not switched from the RRC connected state tothe RRC inactive state.

In addition, a method for determining, by the RAN node based on theseparameters, whether to switch the terminal device from the RRC connectedstate to the RRC inactive state is similar to that in the prior art, anddetails are not described herein one by one.

The determining, by the RAN node, an RNA of the terminal device based onsecond location information and specified area related information ofthe terminal device in step 701 may use the following twoimplementations:

First manner: The specified area related information includes thelocation area identifier list corresponding to the specified area. Whena location indicated by the second location information is within anarea indicated by the location area identifier list corresponding to thespecified area, the RAN node determines the RNA based on first referenceinformation. The RNA is included in the specified area, and the firstreference information includes at least registration area information ofthe terminal device.

The registration area of the terminal device is a registration areaindicated by the registration area information of the terminal devicethat is sent by the AMF node to the RAN node. The registration area isan area allocated by the AMF node to the terminal device, and is used tomanage a location of the terminal device. When the terminal device movesout of the registration area, the terminal device needs to report newestlocation information of the terminal device to the AMF node.

The first reference information may further include any one or more ofthe following information:

whether a RAN node adjacent to a RAN node accessed by the terminaldevice supports the RRC inactive state of the terminal device;

whether there is an Xn interface between the RAN node accessed by theterminal device and the adjacent RAN node; and

expected handover behavior (Expected HO behavior) information of theterminal device.

For example, if the RAN node adjacent to the RAN node accessed by theterminal device supports the RRC inactive state of the terminal device,the RNA may include both a service area of the RAN node accessed by theterminal device and a service area of the RAN node adjacent to the RANnode accessed by the terminal device.

If there is an Xn interface between the RAN node accessed by theterminal device and the adjacent RAN node, the RNA may include both aservice area of the RAN node accessed by the terminal device and aservice area of the RAN node adjacent to the RAN node accessed by theterminal device.

The expected handover behavior information of the terminal device may bean expected handover period of the terminal device. For example, if theterminal device moves fast, a handover time is short. To avoid frequentRNA handovers of the terminal device, a relatively large RNA may be set.

The RAN node may determine an area based on the first referenceinformation. An overlapping area between the area and the LADN SA is theRNA of the terminal device. Optionally, the RNA may be any sub areawithin an overlapping area between the area and the LADN SA. Forexample, as shown in FIG. 8, an area 1 is an area determined by the RANnode based on the first reference information, and the RNA of theterminal device that is determined by the RAN node may be a shadow areain FIG. 8 or any sub area within a shadow area.

Second manner: The specified area related information includes LADN SArelated information, and the LADN SA related information includes a datanetwork name DNN corresponding to the LADN SA. The RAN node determines,based on the DNN, and a mapping relationship between the DNN and thelocation area identifier list corresponding to the LADN SA, a locationarea identifier list corresponding to the LADN SA. When a locationindicated by the second location information is within an area indicatedby the location area identifier list corresponding to the LADN SA, theRAN node determines the RNA based on second reference information. Thesecond reference information includes at least registration areainformation of the terminal device, and the RNA is included in the LADNSA.

The second reference information may further include any one or more ofthe following information:

whether a RAN node adjacent to a RAN node accessed by the terminaldevice supports the RRC inactive state of the terminal device;

whether there is an Xn interface between the RAN node accessed by theterminal device and the adjacent RAN node; and

expected handover behavior information of the terminal device.

It should be noted that, the first reference information and the secondreference information may be the same, and a method for determining theRNA by the RAN node based on the second reference information is thesame as a method for determining the RNA by the RAN node based on thefirst reference information. Details are not described herein again.

The second location information may be information about a cell that theterminal device camps on or information about a tracking area that theterminal device camps on when the terminal device is switched from theRRC connected state to the RRC inactive state.

A method for obtaining the second location information may be asfollows: The RAN node can obtain, by receiving a message sent by theterminal device, information about a cell accessed by the terminaldevice, and then determine the second location information of theterminal device based on the information about the cell.

702: The RAN node sends a second message to the terminal device.

The second message is used to release an RRC connection between theterminal device and the RAN node, and the second message carries theRNA. For example, the second message may be an RRC connection releasemessage.

703: The terminal device receives a second message, and switches a stateof the terminal device from the RRC connected state to the RRC inactivestate based on the second message, and stores the RNA of the terminaldevice.

Further, when the terminal device is in the RRC inactive state, thelocation of the terminal device may change, and the method may furtherinclude step 704 to step 707.

704: When determining that the terminal device moves out of the RNA, theterminal device sends a third message to the RAN node.

Correspondingly, the RAN node receives the third message from theterminal device.

The third message is used to request, when the terminal device moves outof the RNA, to restore the RRC connection between the terminal deviceand the RAN node. For example, the third message may be an RRCconnection restoration request message.

A method for determining, by the terminal device, that the terminaldevice moves out of the RNA is as follows: The terminal device maydetermine location information of the terminal device based on theinformation about the accessed cell. Because the terminal device storesthe RNA, the terminal device can determine whether the locationindicated by the location information of the terminal device is withinthe RNA, and when determining that the location indicated by thelocation information of the terminal device is not within the RNA, candetermine that the terminal device moves out of the RNA.

It should be noted that, if the terminal device moves out of the RNA,the terminal device re-access the RAN node. If the re-accessed RAN nodedetermines that the terminal device still needs to be switched to theRRC inactive state, the RAN node re-sets an RNA for the terminal device.

705: The RAN node sends a response message of the third message to theterminal device.

The response message of the third message is used to instruct theterminal device to establish the RRC connection to the RAN node.

706: The terminal device receives the response message of the thirdmessage, and switches the state of the terminal device from the RRCinactive state to the RRC connected state.

707: The RAN node updates location information of the terminal device tothe first location information.

An execution order of step 705 and step 707 may be adjusted, and is notlimited.

In a process in which the terminal device moves out of the RNA, thelocation information of the terminal device may change, and when theterminal device is in the RRC inactive state, the RAN node cannot obtainthe location information of the terminal device. Therefore, to ensureaccuracy of the location information of the terminal device that isstored in the RAN node, after the RAN node receives the third message orafter the terminal device restores the RRC connection to the RAN node,the RAN node may obtain the information about the cell of the terminaldevice, and determine the first location information of the terminaldevice based on the information about the cell of the terminal device,and update the location information of the terminal device to the firstlocation information.

For example, when the terminal device sends a message to the RAN node byusing a channel, the RAN node may determine, based on a frequency orother information corresponding to the channel, the cell accessed by theterminal device, and further determine location information of the cellas the first location information of the terminal device.

Optionally, after updating the location information of the terminaldevice to the first location information, the RAN node can perform step602.

According to the communications method provided in the foregoingimplementation scenario, the RAN node determines the RNA with referenceto the specified area related information, so that the determined RNA isincluded in the specified area. Therefore, a case in which the terminaldevice moves out of the specified area but is still within the RNA isavoided, and when the specified area is the LADN SA, a problem that theterminal device in the RRC inactive state can still receive LADN dataafter moving out of the LADN SA is avoided.

An embodiment of this application further provides a communicationsmethod. As shown in FIG. 9, the method includes the following steps.

901: An AMF node sends a first message to a RAN node.

Correspondingly, the RAN node receives the first message.

The first message is used to instruct, when the RAN node determines toswitch a terminal device from an RRC connected state to an RRC inactivestate, the RAN node to send, to the AMF node, a first notificationmessage used to notify a state of the terminal device. For example, aname of the first message has the foregoing indication function. Foranother example, the first message carries indication information, andthe indication information has the foregoing indication function.

For example, the first message may carry first indication information,and the first indication information is used to instruct, when the RANnode determines to switch the terminal device from the RRC connectedstate to the RRC inactive state, the RAN node to send the firstnotification message to the AMF node. The first indication informationmay be dedicated to the foregoing indication function, that is, anexplicit indication manner. For example, the first indicationinformation is indicated by using one bit, and when the bit is set to 1,the first indication information instructs, when the RAN node determinesto switch the terminal device from the RRC connected state to the RRCinactive state, to send, to the AMF node, the first notification messageused to notify the state of the terminal device. Alternatively, thefirst indication information may be an implicit indication manner. Forexample, the first indication information includes specified arearelated information, and the specified area related information is usedto indicate a specified area of the terminal device.

The specified area may be an LADN SA, or a location reporting area, oran area of interest of an SMF node.

Optionally, the specified area related information includes a locationarea identifier list corresponding to the specified area. The locationarea identifier list may be a cell identifier list or a TAI list.

Optionally, the specified area related information includes LADN SArelated information, and the LADN SA related information may include alocation area identifier list corresponding to the LADN SA and/or a DNNcorresponding to the LADN SA.

It should be noted that, for related terms such as the specified area,refer to related descriptions in the embodiment shown in FIG. 6, anddetails are not described again.

902: When the RAN node determines to switch a terminal device from anRRC connected state to an RRC inactive state, the RAN node sends a firstnotification message to the AMF node based on the first message.

The RAN node may determine, based on whether data is transmitted betweenthe terminal device and the RAN node within a specified time period,whether to switch the terminal device from the RRC connected state tothe RRC inactive state. If no data is transmitted between the terminaldevice and the RAN node within the specified time period, it may bedetermined that the terminal device is to be switched from the RRCconnected state to the RRC inactive state. For a related method fordetermining, by the RAN node, to switch the terminal device from the RRCconnected state to the RRC inactive state, refer to descriptions belowstep 701.

A method for sending, by the RAN node, the first notification message tothe AMF node based on the first message may include:

when the first indication information is used to instruct, when the RANnode determines to switch the terminal device from the RRC connectedstate to the RRC inactive state, the RAN node to send the firstnotification message to the AMF node, sending the first notificationmessage to the AMF node.

903: The AMF node receives the first notification message from the RANnode, and sends a second notification message to an SMF node based onthe first notification message.

Correspondingly, the SMF node receives the first notification messagefrom the AMF node.

The second notification message is used to notify the SMF node of thestate of the terminal device.

Optionally, step 903 includes two implementations:

First implementation: The first notification message is the same as thesecond notification message. To be specific, after receiving the firstnotification message from the RAN node, the AMF node forwards the firstnotification message to the SMF node.

Second implementation: The AMF node receives the first notificationmessage from the RAN node, reads content in the first message, and thenadds, to the second notification message, information that is in thefirst notification message and that is used to indicate the state of theterminal device, and sends the second notification message to the SMFnode. For example, the second notification message may be a stateswitching notification message, or a Namf_EventExposure_Notify messagesent by the AMF node to the SMF node.

According to the communications method provided in the foregoingembodiment, the AMF node may notify the RAN node in advance; when it isdetermined that the terminal device is to be switched from the RRCconnected state to the RRC inactive state, the notification message usedto notify the state of the terminal device needs to be sent to the AMFnode; then the AMF node sends, to the SMF node, the notification messageused to notify the state of the terminal device; and when receiving thenotification message, the SMF node can determine that the terminaldevice is already in the RRC inactive state, and does not send LADN datato the terminal device, thereby avoiding a problem that the terminaldevice in the RRC inactive state can still receive LADN data aftermoving out of the LADN SA.

Optionally, in an implementation scenario of the foregoing embodimentshown in FIG. 9, as shown in FIG. 10, after step 903, the method furtherincludes step 1001 to step 1005.

1001: The SMF node receives the second notification message, and whenthe second notification message is used to notify that a state of theterminal device is the RRC inactive state, the SMF node sends a fifthmessage to a UPF node, where the fifth message is used to request theUPF node to release a PDU session resource of the terminal device.

Correspondingly, the UPF node receives the fifth message.

It should be noted that, after receiving the fifth message, the UPF nodereleases the PDU session resource of the terminal device based on thefifth message.

1002: The UPF node sends a sixth message to the SMF node.

Correspondingly, the SMF node receives the sixth message from the UPFnode.

The sixth message is used to notify the SMF node that the UPF nodealready releases the PDU session resource of the terminal device, andthe sixth message carries a PDU session identifier of a PDU session ofthe terminal device.

1003: The SMF node sends a seventh message to the AMF node, where theseventh message carries a PDU session identifier, and the seventhmessage is used to instruct the RAN node to release a PDU sessionresource corresponding to the PDU session identifier.

1004: The AMF node receives the seventh message from the SMF node, andsends a third message to the RAN node based on the seventh message,where the third message carries the PDU session identifier, and thethird message is used to instruct the RAN node to release the PDUsession resource corresponding to the PDU session identifier.

1005: The RAN node receives the third message from the AMF node, andreleases, based on the third message, the PDU session resourcecorresponding to the PDU session identifier.

According to the foregoing implementation scenario, when determiningthat the state of the terminal device is the RRC inactive state, the SMFnode may instruct the UPF node to release the PDU session resource, andfurther instruct, by exchanging signaling, the RAN node to release thePDU session resource. In this way, when the terminal device moves out ofthe specified area, there is no PDU session resource used for sendingrelated service data, for example, the problem that the terminal devicecan still receive LADN data when moving out of the LADN SA is avoided.

Optionally, in another implementation scenario of the embodiment shownin FIG. 9, as shown in FIG. 11, after the RAN node receives the firstmessage from the AMF node in step 901, the method further includes step1101 and step 1102.

1101: When the RAN node determines to switch the terminal device fromthe RRC connected state to the RRC inactive state, the RAN nodedetermines an RNA of the terminal device based on location informationof the terminal device.

For example, the RAN node determines a cell or a tracking area that isindicated by the location information of the terminal device as the RNAof the terminal device.

For example, the RAN node determines the RNA of the terminal devicebased on the location information of the terminal device and firstreference information.

A location indicated by the location information of the terminal deviceis within the determined RNA of the terminal device.

The first reference information includes at least registration areainformation of the terminal device. The registration area information isused to indicate a registration area of the terminal device, and theregistration area is an area allocated by the AMF node to the terminaldevice and is used to manage a location of the terminal device. When theterminal device moves out of the registration area, the terminal devicereports newest location information of the terminal device to the AMFnode. In addition, the registration area information of the terminaldevice may be sent by the AMF node to the RAN node.

Further, the first reference information may further include any one ormore of the following information:

whether a RAN node adjacent to a RAN node accessed by the terminaldevice supports the RRC inactive state of the terminal device;

whether there is an Xn interface between the RAN node accessed by theterminal device and the adjacent RAN node; and

expected handover behavior information of the terminal device.

For example, if the RAN node adjacent to the RAN node accessed by theterminal device supports the RRC inactive state of the terminal device,the RNA may include both a service area of the RAN node accessed by theterminal device and a service area of the RAN node adjacent to the RANnode accessed by the terminal device.

If there is an Xn interface between the RAN node accessed by theterminal device and the adjacent RAN node, the RNA may include both aservice area of the RAN node accessed by the terminal device and aservice area of the RAN node adjacent to the RAN node accessed by theterminal device.

The expected handover behavior information of the terminal device may bean expected handover period of the terminal device. For example, if theterminal device moves fast, a handover time is short. To avoid frequentRNA handovers of the terminal device, a relatively large RNA may be set.

1102: The RAN node sends a second message to the terminal device, wherethe second message is used to instruct the terminal device to release anRRC connection between the terminal device and the RAN node, and thesecond message carries the RNA.

Optionally, in an implementation scenario of the embodiment shown inFIG. 11, after a procedure shown in FIG. 11 is performed, if the SMFnode receives a downlink data notification (downlink data notification,DDN), the RRC connection between the terminal device and the RAN node isre-established. As shown in FIG. 12, the method includes the followingsteps.

1103: The AMF node sends a fourth message to the RAN node.

The fourth message is used to request to establish the RRC connectionbetween the terminal device and the RAN node. For example, the fourthmessage may be an N2 message.

For example, when obtaining downlink LADN data, the UPF node sends a DDNmessage to the SMF node. The DDN message is used to notify the SMF nodethat the UPF node obtains the downlink LADN data. After receiving theDDN message, the SMF node sends an N11 message to the AMF node. The N11message is used to request to establish a user plane resource. Afterreceiving the N11 message, the AMF node sends the fourth message to theRAN node.

1104: The RAN node receives the fourth message from the AMF node, andinstructs the terminal device to establish the RRC connection betweenthe terminal device and the RAN node.

For example, the RAN node instructs, by sending a paging message to theterminal device, the terminal device to establish the RRC connectionbetween the terminal device and the RAN node. For example, afterreceiving the fourth message, the RAN node initiates paging to theterminal device. After receiving the paging message from the RAN node,the terminal device sends an RRC connection restoration request to theRAN node. After receiving the RRC connection restoration request, theRAN node may obtain information about a cell accessed by the terminaldevice, and determine the location information of the terminal devicebased on the information about the cell.

1105: When the RAN node determines, based on specified area relatedinformation and location information of the terminal device, that theterminal device moves out of a specified area, the RAN node sends thelocation information of the terminal device or first indicationinformation to the AMF node or the SMF node, where the first indicationinformation is used to indicate that the terminal device already movesout of the specified area.

The specified area related information may be carried in the firstmessage, and the specified area related information is used to indicatethe specified area of the terminal device. The specified area may bespecifically an LADN SA, or a location reporting area (LocationReporting area), or an area of interest (Area of interest) of the SMFnode.

For a specific implementation of step 1105, refer to relateddescriptions of step 602, and details are not described herein again.

Optionally, after the sending, by the RAN node, the location informationof the terminal device or first indication information to the AMF nodeor the SMF node, the method further includes the following steps.

If the RAN node sends the location information of the terminal device tothe AMF node in step 1105, step 1106 a needs to be performed.

The location information of the terminal device may be obtained in amanner in step 1104, and details are not described again.

1106 a: When the AMF node determines, based on the specified arearelated information and the location information of the terminal device,that the terminal device moves out of the specified area, the AMF nodesends the first indication information to the SMF node, where the firstindication information is used to indicate that the terminal devicealready moves out of the specified area.

Optionally, if the RAN node sends the first indication information tothe AMF node in step 1105, step 1106 a may be replaced with 1106 b.

1106 b: The AMF node sends the first indication information to the SMFnode, where the first indication information is used to indicate thatthe terminal device already moves out of the specified area of theterminal device.

Further optionally, after step 1106 a or step 1106 b, the method mayfurther include the following steps.

1107: The SMF node sends an N4 message to the UPF node, where the N4message is used to instruct the UPF node to prolong buffering ofdownlink data or discard downlink data.

For example, the N4 message is used to instruct the UPF node to prolongbuffering of downlink LADN data or discard downlink LADN data.

1108: The SMF node receives the N4 message, and prolongs buffering ofthe downlink data or discards the downlink data based on the N4 message.

Optionally, step 1105 may be replaced with 1105 a.

1105 a: When the RAN node determines, based on the specified arearelated information and the location information of the terminal device,that the terminal device moves out of the specified area, the RAN nodesends a response message of the fourth message to the AMF node.

The response message of the fourth message is used by the RAN node toreject establishment of the RRC connection between the terminal deviceand the RAN node.

Correspondingly, the AMF node receives the response message of thefourth message from the RAN node.

Further optionally, after step 1105 a, step 1107 and step 1108 areperformed.

According to the communications method provided in the foregoingimplementation scenario, when obtaining downlink data of the terminaldevice, the UPF node notifies the RAN node by using the SMF node and theAMF node, so that the RAN node instructs the terminal device toestablish the RRC connection between the terminal device and the RANnode, and further, the RAN node may determine the location informationof the terminal device, and if the RAN node determines, based on thelocation information of the terminal device, that the terminal devicealready moves out of the specified area, the RAN node reports relatedinformation or a related message to the AMF node or the SMF node, sothat the SMF node instructs the UPF node to release downlink LADN dataor prolong buffering of downlink LADN data, thereby ensuring that theterminal device does not receive the downlink LADN data when moving outof the specified area.

An embodiment of this application further provides a communicationsmethod. As shown in FIG. 13, the method includes the following steps.

1301: A RAN node determines that a terminal device switches from an RRCconnected state to an RRC inactive state.

For example, the RAN node may determine, based on whether data istransmitted between the terminal device and the RAN node within aspecified time period, whether to switch the terminal device from theRRC connected state to the RRC inactive state. If no data is transmittedbetween the terminal device and the RAN node within the specified timeperiod, it may be determined that the terminal device is to be switchedfrom the RRC connected state to the RRC inactive state.

For a specific implementation of step 1301, refer to relateddescriptions in the embodiment shown in FIG. 6, FIG. 7, or FIG. 8, anddetails are not described again.

1302: The RAN node sends, to an AMF node, a notification message used tonotify a state of the terminal device.

For example, the state of the terminal device may be the RRC inactivestate.

Correspondingly, the AMF node receives the notification message from theRAN node.

According to the communications method provided in this embodiment, whendetermining that the terminal device switches from the RRC connectedstate to the RRC inactive state, the RAN node sends, to the AMF node,the notification message used to notify the state of the terminaldevice; and when receiving the notification message, the AMF node candetermine that the terminal device is already in the RRC inactive state,and does not send LADN data to the terminal device, thereby avoiding aproblem that the terminal device in the RRC inactive state can stillreceive LADN data after moving out of an LADN SA.

Optionally, in an implementation scenario of the foregoing embodiment,as shown in FIG. 14, before step 1301, the method further includes thefollowing steps.

1401: The RAN node determines an RNA of the terminal device based onlocation information of the terminal device.

For step 1401, refer to related descriptions of step 1101, and detailsare not described again.

1402: The RAN node sends a first message to the terminal device.

Correspondingly, the terminal device receives the first message.

The first message is used to instruct the terminal device to release anRRC connection to the RAN node, and the first message carries the RNA.

Optionally, in another implementation scenario of the foregoingembodiment, after step 1302, the method further includes the followingsteps.

1403: The AMF node sends, to an SMF node, the notification message usedto notify the state of the terminal device.

1404: The SMF node receives the notification message from the AMF node,and when the notification message is used to notify that the state ofthe terminal device is the RRC inactive state, the SMF node sends asecond message to a UPF node.

The second message is used to request the UPF node to release a PDUsession resource of the terminal device. For example, the first messagemay be a PDU session release request message.

1405: The UPF node receives the second message, and releases a PDUsession resource of the terminal device.

1406: The UPF node sends a third message to the SMF node.

The third message is used to notify the SMF node that the UPF nodealready releases the PDU session resource of the terminal device, andthe third message includes a PDU session identifier. The PDU sessionidentifier is used to indicate a PDU session used to transmit data ofthe terminal device. For example, the third message may be a PDU sessionrelease response.

1407: The SMF node sends a fourth message to the AMF node.

The fourth message carries the PDU session identifier carried in thethird message in step 1406, and the fourth message is used to triggerthe AMF node to instruct the RAN node to release a PDU session resourcecorresponding to the PDU session identifier.

1408: The AMF node receives the fourth message, and sends a fifthmessage to the RAN node.

The fifth message includes the PDU session identifier carried in thefourth message in step 1407. The fifth message is used to instruct theRAN node to release the PDU session resource corresponding to the PDUsession identifier.

1409: The RAN node receives the fifth message, and releases a PDUsession resource corresponding to the PDU session identifier.

It should be noted that, the foregoing embodiments may be mutuallylearned and referenced, and same or similar descriptions are notrepeated.

The solutions provided in the embodiments of the present invention aremainly described above from the perspective of interaction between theRAN node, the AMF node, and the SMF node. It may be understood that, theRAN node, the AMF node, and the SMF node each include a correspondinghardware structure and/or software module that performs variousfunctions. A person skilled in the art should be easily aware that, incombination with the units and algorithm steps of the examples describedin the embodiments disclosed in this specification, this application canbe implemented by hardware or a combination of hardware and computersoftware. Whether a function is performed by hardware or by computersoftware driving hardware depends on particular applications and designconstraint conditions of the technical solutions. A person skilled inthe art may use different methods to implement the described functionsfor each particular application, but it should not be considered thatthe implementation goes beyond the scope of the present invention.

In the embodiments of this application, functional modules in the SMFnode may be divided according to the foregoing method example. Forexample, the functional modules may be divided corresponding to thefunctions. Alternatively, two or more functions may be integrated into aprocessing module. The integrated module may be implemented in a form ofhardware, or may be implemented in a form of a software functionalmodule. It should be noted that division of the modules in theembodiments of this application is an example, and is merely logicalfunction division. During actual implementation, there may be anotherdivision manner.

When the functional modules are divided by using correspondingfunctions, an embodiment of this application provides a communicationsapparatus. The apparatus may be implemented as the RAN node in theforegoing embodiment. As shown in FIG. 15, FIG. 15 is a possibleschematic structural diagram of the RAN node in the foregoingembodiment. The RAN node includes a receiving module 1501, a determiningmodule 1502, and a sending module 1503.

The receiving module 1501 is configured to support receiving the firstmessage in step 601 in FIG. 6 and FIG. 7 and the third message in step704 in FIG. 7 by the RAN node. The determining module 1502 is configuredto support the RAN node to perform step 602 in FIG. 6 and step 701 inFIG. 7. The sending module 1503 is configured to support the RAN node toperform step 602 in FIG. 6 and step 702, step 705, and step 602 in FIG.7.

Optionally, the RAN node further includes an update module 1504.

The update module 1504 is configured to support the RAN node to performstep 707 in FIG. 7.

As shown in FIG. 16, FIG. 16 is another possible schematic structuraldiagram of a RAN node. The RAN node includes a receiving module 1601, adetermining module 1602, and a sending module 1603.

The receiving module 1601 is configured to support receiving the firstmessage in step 901 in FIG. 9, FIG. 10, and FIG. 11, the third messagein step 1004 in FIG. 10 and FIG. 11, and the fourth message in step 1103in FIG. 14 by the RAN node. The determining module 1602 is configured tosupport the RAN node to perform step 902 in FIG. 9, FIG. 10, and FIG.11, step 1101 in FIG. 11, and step 1105 and step 1105 a in FIG. 12. Thesending module 1603 is configured to support the RAN node to performstep 902 in FIG. 9, FIG. 10, and FIG. 11 and step 1105 in FIG. 12.

Optionally, the RAN node further includes a release module 1604.

The release module 1604 is configured to support the RAN node to performstep 1005 in FIG. 10 and FIG. 11.

As shown in FIG. 17, FIG. 17 is another possible schematic structuraldiagram of a RAN node. The RAN node includes a determining module 1701and a notification module 1702.

The determining module 1701 is configured to support the RAN node toperform step 1301 in FIG. 13 and step 1401 and step 1301 in FIG. 14. Thenotification module 1702 is configured to support the RAN node toperform step 1302 in FIG. 13.

When the functional modules are divided by using correspondingfunctions, an embodiment of this application provides a communicationsapparatus. The apparatus may be implemented as the AMF node in theforegoing embodiment. As shown in FIG. 18, FIG. 18 is a possibleschematic structural diagram of the AMF node in the foregoingembodiment. The AMF node includes a sending module 1801 and a receivingmodule 1802.

The sending module 1801 is configured to support the AMF node to performstep 601 in FIG. 6, step 601 in FIG. 7, step 901 and step 903 in FIG. 9,step 901, step 903, and step 1004 in FIG. 10, step 901, step 903, andstep 1004 in FIG. 11, step 1103, step 1106 a, and step 1106 b in FIG.12, and step 1403 in FIG. 14.

The receiving module 1802 is configured to support receiving the firstlocation information or the first indication information in step 602 inFIG. 6 and FIG. 7, the first notification message in step 902 in FIG. 9,FIG. 10, and FIG. 11, the seventh message in step 1003 in FIG. 10 andFIG. 11, the location information of the terminal device or the firstindication information in step 1105 in FIG. 12, the notification messagein step 1302 in FIG. 13 and FIG. 14, and the fourth message in step 1407in FIG. 14 by the AMF node.

Optionally, the apparatus further includes a determining module 1803.

The determining module 1803 is configured to support the AMF node toperform step 1106 a in FIG. 12.

When the functional modules are divided by using correspondingfunctions, an embodiment of this application provides a communicationsapparatus. The apparatus may be implemented as the SMF node in theforegoing embodiment. As shown in FIG. 19, FIG. 19 is a possibleschematic structural diagram of the SMF node in the foregoingembodiment. The SMF node includes a receiving module 1901 and a sendingmodule 1902.

The receiving module 1901 is configured to support the SMF node toperform step 602 in FIG. 6 and FIG. 7, and receiving the secondnotification message in step 903 in FIG. 9, FIG. 10, and FIG. 11, thelocation information of the terminal device or the first indicationinformation in step 1105 and the first indication information in step1106 a or step 1106 b in FIG. 12, and the notification message in step1403 and the third message in step 1046 in FIG. 13.

The sending module 1902 is configured to support sending the fifthmessage in FIG. 9 and FIG. 10 by the SMF node, and is further configuredto support the SMF node to perform step 1003 in FIG. 9 and FIG. 10, step1107 in FIG. 12, and step 1407 in FIG. 14.

For all related content of the steps in the foregoing methodembodiments, refer to function descriptions of the correspondingfunctional modules, and details are not described herein again.

As shown in FIG. 20, a RAN node 2000 may include a memory 2001, aprocessor 2002, a communications interface 2003, and a bus 2004. The bus2004 is configured to implement a connection and mutual communicationbetween these apparatuses.

The communications interface 2003 may be implemented by using anantenna, and may be configured to exchange data with an external networkelement, for example, the communications interface 2003 may receive/senda data packet or other information from/to an AMF device.

The processor 2002 may be a central processing unit (CPU), or anapplication-specific integrated circuit (ASIC), or one or moreintegrated circuits configured to implement the embodiments of thepresent invention, for example, one or more microprocessors (DSP) or oneor more field programmable gate arrays (FPGA). The processor 2002 has aprocessing and management function. Specifically, the processor 2002 mayprocess received data or information sent by the AMF device, a UPFdevice, or a PCRF device, or process information or data sent by anotherdevice.

The memory 2001 may be a read-only memory (ROM) or another type ofstatic storage device that can store static information and aninstruction, a random access memory (RAM) or another type of dynamicstorage device that can store information and an instruction, or may bean electrically erasable programmable read-only memory (EEPROM), acompact disc read-only memory (CD-ROM), or another optical disk storage,an optical disc storage (including a compact disc, a laser disc, anoptical disc, a digital versatile disc, a Blu-ray disc, and the like), amagnetic disk storage medium or another magnetic storage device, or anyother medium that can carry or store expected program code in a form ofan instruction or a data structure and can be accessed by a computer,but is not limited thereto. The memory 2001 may exist independently, andis connected to the processor 2002 by using the bus 2004. The memory2001 may alternatively be integrated with the processor 2002.

It should be noted that, the receiving module 1501 and the sendingmodule 1503 shown in FIG. 15, the receiving module 1601 and the sendingmodule 1603 shown in FIG. 16, and the notification module 1702 shown inFIG. 17 may be integrated into the communications interface 2003 shownin FIG. 20, so that the communications interface 2003 performs specificfunctions of the receiving module 1501 and the sending module 1503 shownin FIG. 15, the receiving module 1601 and the sending module 1603 shownin FIG. 16, and the notification module 1702 shown in FIG. 17. Thedetermining module 1502 and the update module 1504 shown in FIG. 15, thedetermining module 1602 and the release module 1604 shown in FIG. 16,and the determining module 1701 shown in FIG. 17 may be integrated intothe processor 2002 shown in FIG. 20, so that the processor 2002 performsspecific functions of the determining module 1502 and the update module1504 shown in FIG. 15, the determining module 1602 and the releasemodule 1604 shown in FIG. 16, and the determining module 1701 shown inFIG. 17.

As shown in FIG. 21, an AMF node 2100 may include a memory 2101, aprocessor 2102, a communications interface 2103, and a bus 2104. The bus2104 is configured to implement a connection and mutual communicationbetween these apparatuses.

The communications interface 2103 may be implemented by using anantenna, and may be configured to exchange data with an external networkelement, for example, the communications interface 2103 may receive/senda data packet or other information from/to an AMF device.

The processor 2102 may be a central processing unit (CPU), or anapplication-specific integrated circuit (ASIC), or one or moreintegrated circuits configured to implement the embodiments of thepresent invention, for example, one or more microprocessors (DSP) or oneor more field programmable gate arrays (FPGA). The processor 2102 has aprocessing and management function. Specifically, the processor 2102 mayprocess received data or information sent by the AMF device, a UPFdevice, or a PCRF device, or process information or data sent by anotherdevice.

The memory 2101 may be a read-only memory (ROM) or another type ofstatic storage device that can store static information and aninstruction, a random access memory (RAM) or another type of dynamicstorage device that can store information and an instruction, or may bean electrically erasable programmable read-only memory (EEPROM), acompact disc read-only memory (CD-ROM), or another optical disk storage,an optical disc storage (including a compact disc, a laser disc, anoptical disc, a digital versatile disc, a Blu-ray disc, and the like), amagnetic disk storage medium or another magnetic storage device, or anyother medium that can carry or store expected program code in a form ofan instruction or a data structure and can be accessed by a computer,but is not limited thereto. The memory 2101 may exist independently, andis connected to the processor 2104 by using the bus 2102. The memory2101 may alternatively be integrated with the processor 2102.

It should be noted that, the sending module 1801 and the receivingmodule 1802 shown in FIG. 18 may be integrated into the communicationsinterface 2203 shown in FIG. 22, so that the communications interface2203 performs specific functions of the sending module 1801 and thereceiving module 1802 shown in FIG. 18. The determining module 1803shown in FIG. 18 may be integrated into the processor 2202 shown in FIG.22, so that the processor 2202 performs a specific function of thedetermining module 1803 shown in FIG. 18.

As shown in FIG. 22, an SMF node 2200 may include a memory 2201, aprocessor 2202, a communications interface 2203, and a bus 2204. The bus2204 is configured to implement a connection and mutual communicationbetween these apparatuses.

The communications interface 2203 may be implemented by using anantenna, and may be configured to exchange data with an external networkelement, for example, the communications interface 2203 may receive/senda data packet or other information from/to an AMF device.

The processor 2202 may be a central processing unit (CPU), or anapplication-specific integrated circuit (ASIC), or one or moreintegrated circuits configured to implement the embodiments of thepresent invention. For example, one or more microprocessors (DSP) or oneor more field programmable gate arrays (FPGA). The processor 2202 has aprocessing and management function. Specifically, the processor 2202 mayprocess received data or information sent by the AMF device, a UPFdevice, or a PCRF device, or process information or data sent by anotherdevice.

The memory 2201 may be a read-only memory (ROM) or another type ofstatic storage device that can store static information and aninstruction, a random access memory (RAM) or another type of dynamicstorage device that can store information and an instruction, or may bean electrically erasable programmable read-only memory (EEPROM), acompact disc read-only memory (CD-ROM), or another optical disk storage,an optical disc storage (including a compact disc, a laser disc, anoptical disc, a digital versatile disc, a Blu-ray disc, and the like), amagnetic disk storage medium or another magnetic storage device, or anyother medium that can carry or store expected program code in a form ofan instruction or a data structure and can be accessed by a computer,but is not limited thereto. The memory 2201 may exist independently, andis connected to the processor 2204 by using the bus 2202. The memory2201 may alternatively be integrated with the processor 2202.

It should be noted that, the receiving module 1901 and the sendingmodule 1902 shown in FIG. 19 may be integrated into the communicationsinterface 2203 shown in FIG. 22, so that the communications interface2203 performs specific functions of the receiving module 1901 and thesending module 1902 shown in FIG. 19.

The methods or algorithm steps described with reference to the contentdisclosed in this application may be implemented in a hardware manner,or may be implemented in a manner of executing a software instruction bya processor. The software instruction may include a correspondingsoftware module. The software module may be stored in a random accessmemory (RAM), a flash memory, a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM), an electrically erasableprogrammable read-only memory (EEPROM), a register, a hard disk, aremovable hard disk, a compact disc read-only memory (CD-ROM), or astorage medium in any other forms well-known in the art. A storagemedium used as an example is coupled to the processor, so that theprocessor can read information from the storage medium, and can writeinformation into the storage medium. Certainly, alternatively, thestorage medium may be a part of the processor. The processor and thestorage medium may be located in an ASIC. In addition, the ASIC may belocated in a core network interface device. Certainly, the processor andthe storage medium may exist in the core network interface device asdiscrete components.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented through some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork devices. Some or all of the units may be selected based onactual needs to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of the presentinvention may be integrated into one processing unit, or each of thefunctional units may exist alone, or two or more units are integratedinto one unit. The integrated unit may be implemented in a form ofhardware, or may be implemented in a form of hardware in addition to asoftware functional unit.

Based on the foregoing descriptions of the implementations, a personskilled in the art may clearly understand that this application may beimplemented by software in addition to necessary universal hardware orcertainly by hardware only. In most circumstances, the former is apreferred implementation. Based on such an understanding, the technicalsolutions of this application essentially or the part contributing tothe prior art may be implemented in a form of a software product. Thecomputer software product is stored in a readable storage medium, suchas a floppy disk, a hard disk, or an optical disc of a computer, andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, or a network device) to performthe methods described in the embodiments of this application.

The foregoing descriptions are merely specific embodiments of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement disclosed in this applicationshall fall within the protection scope of this application. Therefore,the protection scope of this application shall be subject to theprotection scope of the claims.

What is claimed is:
 1. A communications method, comprising: sending, byan access and mobility management function (AMF) node, a first messageto a radio access network (RAN) node, wherein the first messagecomprises specified area related information of a terminal device, andthe specified area related information indicates a specified area of theterminal device, wherein the specified area related informationcomprises a location area identifier list corresponding to the specifiedarea, and the location area identifier list is a cell identifier (CellID) list or a tracking area identity (TAI) list; receiving, by the RANnode, the first message; after receiving the first message, determining,by the RAN node based on the specified area related information andfirst location information of the terminal device, that the terminaldevice moves out of the specified area, wherein determining, by the RANnode based on the specified area related information and the firstlocation information of the terminal device, that the terminal devicemoves out of the specified area comprises: in case that a locationindicated by the first location information is within none of areasindicated by location area identifiers in the location area identifierlist corresponding to the specified area, determining, by the RAN node,that the terminal device moves out of the specified area; and sending,by the RAN node to the AMF node, first indication information, whereinthe first indication information indicates that the terminal devicemoves out of the specified area.
 2. The communications method accordingto claim 1, wherein the specified area is a local area data networkservice area (LADN SA), a location reporting area, or an area ofinterest.
 3. The communications method according to claim 1, wherein thefirst message comprises a location report control message.
 4. Thecommunications method according to claim 1, wherein before determining,by the RAN node based on the specified area related information and thefirst location information of the terminal device, that the terminaldevice moves out of the specified area, the method further comprises: incase that the RAN node determines to switch the terminal device from aRadio Resource Control (RRC) connected state to an RRC inactive state,determining, by the RAN node, a radio access network notification area(RNA) of the terminal device based on second location information of theterminal device and the specified area related information; and sending,by the RAN node, a second message to the terminal device, wherein thesecond message indicates to release an RRC connection between theterminal device and the RAN node, and the second message carries theRNA.
 5. A communications system, comprising: an access and mobilitymanagement function node; and a radio access network (RAN) node,wherein: the access and mobility management function node is configuredto: send a first message to the RAN node, wherein the first messagecomprises specified area related information of a terminal device, andthe specified area related information indicates a specified area of theterminal device, wherein the specified area related informationcomprises a location area identifier list corresponding to the specifiedarea, and the location area identifier list is a cell identifier (CellID) list or a tracking area identity (TAI) list; and the RAN node isconfigured to: receive the first message; determine that the terminaldevice moves out of the specified area based on the specified arearelated information and first location information of the terminaldevice by determining that the terminal device moves out of thespecified area in case that a location indicated by the first locationinformation is within none of areas indicated by location areaidentifiers in the location area identifier list corresponding to thespecified area; and send first indication information to the access andmobility management function node, wherein the first indicationinformation indicates that the terminal device moves out of thespecified area.
 6. The communications system according to claim 5,wherein the specified area is a local area data network service area(LADN SA), a location reporting area, or an area of interest.
 7. Thecommunications system according to claim 5, wherein the first messagecomprises a location report control message.
 8. The communicationssystem according to claim 5, wherein the RAN node is further configuredto: in case that the RAN node determines to switch the terminal devicefrom a Radio Resource Control (RRC) connected state to an RRC inactivestate, determine a radio access network notification area (RNA) of theterminal device based on second location information of the terminaldevice and the specified area related information; and send a secondmessage to the terminal device, wherein the second message indicates torelease an RRC connection between the terminal device and the RAN node,and the second message carries the RNA.
 9. A communications apparatus,comprising: at least one processor coupled with a non-transitory storagemedium storing executable instructions, wherein the executableinstructions, when executed by the at least one processor, cause thecommunications apparatus to perform operations comprising: receiving afirst message from an access and mobility management function node,wherein the first message comprises specified area related informationof a terminal device, and the specified area related informationindicates a specified area of the terminal device, wherein the specifiedarea related information comprises a location area identifier listcorresponding to the specified area, and the location area identifierlist is a cell identifier (Cell ID) list or a tracking area identity(TAI) list; determining, based on the specified area related informationand first location information of the terminal device, that the terminaldevice moves out of the specified area, wherein determining, based onthe specified area related information and the first locationinformation of the terminal device, that the terminal device moves outof the specified area comprises: in case that a location indicated bythe first location information is within none of areas indicated bylocation area identifiers in the location area identifier listcorresponding to the specified area, determining that the terminaldevice moves out of the specified area; and sending first indicationinformation to the access and mobility management function node, whereinthe first indication information indicates that the terminal devicemoves out of the specified area.
 10. The communications apparatusaccording to claim 9, wherein the specified area is a local area datanetwork service area (LADN SA), a location reporting area, or an area ofinterest.
 11. The communications apparatus according to claim 9, whereinthe first message comprises a location report control message.